BEST IELTS Academic Reading Test 558

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IELTS ACADEMIC READING TEST 558 – PASSAGE – 1

IELTS ACADEMIC READING TEST – 558

READING PASSAGE – 1

EASY COME, EASY GO

The dinosaurs went out with a bang, but they arrived after chaos.

Revolutions have unpredictable outcomes. Who is going to end up in power is rarely obvious at the start. That is as true in biology as it is in politics. Like political revolutions, though, biological ones often follow a predictable course. The old order is destroyed. There is a period of confusion. Then a new ecosystem emerges that looks surprisingly like the old one, but with different actors.

This cycle has happened five times in the history of modern life. The most famous occasion was 65m years ago, when the dinosaurs were wiped out and the mammals emerged victorious from the wreckage. A bigger mass extinction, at the end of the Permian period 25 years ago, killed 70% of the world’s land vertebrates (and 96% of all marine animals) and paved the way for the age of reptiles.

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Exactly which sort of reptile would come out on top, however, was not something that was decided until later – 201.4m years ago, to be precise. This was towards the end of the Triassic period. Then, the ranks of aetosaurs, phytosaurs, shuvosaurs and many other uncrocodile-like relatives of the crocodiles were suddenly thinned, and a previously obscure group came to the fore. The result, once natural selection had done its work over the course of millions of years, was the now familiar cast of Allosaurus, Diplodocus, Triceratops and Tyrannosaurus Rex.

Another one bites the dust:

The dinosaurs were done for, as everybody knows, by a collision with an asteroid. The Permian was curtailed by massive volcanism. But what exactly happened towards the end of the Triassic has been much debated. A study just published in the Proceedings of the National Academy of Sciences, by Jessica Whiteside of Brown University in Rhode Island and her colleagues, pretty well nails it down. It was the geological chaos that created the North Atlantic Ocean.

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Dr Whiteside used fossil evidence sandwiched between layers of lava from some of the earliest eruptions that accompanied the rift. Specifically, she located two sites in what is now eastern North America where a series of giant lakes had formed on the layers of cooled lava and plant matter had accumulated at the bottom of the lakes. Using detailed chemical analysis of waxy molecules extracted from the fossil plants, she examined the carbon isotopes they contained.

Non-radioactive carbon comes in two forms: ¹²C and the heavier (and much rarer form) 13 C. The ratio varies in the atmosphere, depending on where carbon-rich gases, mainly carbon dioxide and methane, are coming from. Dr Whiteside found the ratio yawed around like a drunken sailor as the continents split apart and the lava started pouring out. First, the level of 13C plummeted. Then it shot up again, a long way over the recent historical average, before settling down.

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Crucially, the period of plummeting coincides with a phenomenon called the late Triassic fern spike. This marks precisely – to within a few thousand years – the point of mass extinction on the land. What is believed to have happened is that something killed all the forests and with them the animals that depended on them. Freed from the competition for light (because the shade from the trees had gone), ferns flourished (their spores are ubiquitous in the rocks). Previous work has suggested that the oceans also became acidic at this time. Shelled creatures, whose calcium-carbonate-rich armour tends to dissolve in acid, suddenly became rare.

Put it all together and the probable course of events was this. The initial volcanism as North America split from Europe released carbon dioxide from deep inside the Earth. That produced a greenhouse effect which, in turn, melted seabed structures known as methane clathrates, which trap that gas in ice. This caused a massive release of ¹²C-rich methane into the atmosphere, explaining the initial drop in ¹³C concentrations.

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The methane, being a much more potent greenhouse gas than carbon dioxide, exacerbated things, while the carbon dioxide acidified the oceans, killing most of the animal shellmakers and fertilising the photosynthesis of planktonic plants. The subsequent plankton bloom sucked up the ¹²C and the isotope ratio veered off in the opposite direction.

The greenhouse warming and the acid rain also did for the forests and many of the reptiles. Only once things had settled down could the survivors regroup. New species of trees took over. The forests grew back. And a bunch of hitherto not-so-terrible lizards began their long march.

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Questions 1-6

Do the following statements agree with the information given in Reading Passage 1? In boxes 1-6 on your answer sheet, write

TRUE – if the statement agrees with the information

FALSE – if the statement contradicts the information

NOT GIVEN – if there is no information on this

1. Biological revolutions often run along a course which is puzzling at some stage.

2. That the mammals replaced the dinosaurs was the last ecological revolution ever in modern history.

3. Unexpectedly, the phytosaurs became thinly populated.

4. Natural selection was proved ineffective after being dominant for a long time.

5. The Permian period was more known to the scientists than the Triassic.

6. Dr Whiteside utilised fossil evidence to prove that North American giant lakes had been shaped by volcanism.

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Questions 7-9

Choose the correct letter, A, B, C or D.

7 About 251 m years ago, the percentage of the marine vertebrates that were killed was

A. 70%.

B. 96%.

C. about 67%.

D. unknown.

8. Which of the following is believed NOT to have happened in Triassic?

A. All the forests died out.

B. Armoured animals became extinct.

C. The animals feeding on the forests starved.

D. The oceans turned to be fatal.

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9. Which of the following was generated by greenhouse gas?

A. acid rain

B. the beginning of dinosaurs history

C. the acidification of the oceans

D. the creation of North Atlantic Ocean

Questions 10-14

Choose NO MORE THAN TWO WORDS from the paragraph for each answer.

Various factors were involved in the biological revolutions. It is wellknown that dinosaurs were wiped out by an asteroid’s 10__________ with the earth. 11__________ cut short the Permian period. According to a new research by Jessica Whiteside and her team members, the North Atlantic Ocean could be formed by 12__________ such as the eruptions and the rift. When the continents drifted apart and lava gushed, IJC 13__________ and shot up. And at the same time 14__________ was sent out from the inside of the Earth, generated a greenhouse effect.

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